1. Field of the Invention
The present invention relates to a chemically amplified resist composition and a process for forming a resist pattern by using the same.
2. Description of Related Art
As trends for higher circuit density in microelectronic devices continue, the light source for exposing to a resist film so as to form a fine pattern was originally an ultra-violet but has been shifted to shorter wave length radiation using deep ultra-violet, electron beam X-ray.
In deep ultra-violet lithography, sources may be a high pressure mercury lamp or an excimer laser, but the high pressure mercury lamp has a disadvantageously low output in the wave length range of deep ultra-violet. Accordingly, excimer laser (for example, a wave length of 248 nm when KrF gas is used) is being mainly used in the investigation of a shorter wave length lithography because of high output.
Nevertheless, conventional resists based on a novolak resin using deep ultra violet radiation results in sloped wall profiles and poor resolution because the conventional resist absorbs too much in the deep ultra-violet region.
Accordingly, attempts are being made to provide a resist having excellent sensitivity and high resolution at such a short wave length.
To cope with the above demands, a process for forming a resist pattern has been proposed by IBM using a photo acid generator that generates stong acid upon exposure to radiation in an imagewise configuration. The resist composition contains a photo acid generator in combination with a polymer having a recurrent acid labile pendant. When the resist composition is exposed to radiation, a Bronsted acid is generated from the photo acid generator during the post exposure baking, and will act as a catalyst for successively cleaving the polymer recurrent acid labile pendant groups and changing the polarity of the polymers. The obtained polymers can be developed with an alkali that allows high resolution and does not cause swelling (U.S. Pat. No. 4,491,628 or Japanese Patent Application No. 02-27660). This type of resist is called a chemically amplified resist.
This resist contains a recurrent acid labile pendant group to change the polarity of the polymer and therefore a high sensitivity can be expected using a chemically amplified resist system. The system is a means of improving transparency because such a system requires little of the photosensitive compound as a catalyst.
Nevertheless, resist patterns obtained by the chemically amplified resist as above often have a T-shaped form 1 (a surface inhibition layer 2) as shown in FIG. 1. This T-shaped pattern renders the pattern width uneven and the pattern or the device unreliable.
Moreover, the chemically amplified resists often have poor adhesivity to a substrate, which makes the formation of a fine pattern difficult, i.e., lowers the resolution. It is therefore difficult to reliably form submicron patterns by a chemically amplified resist.
The object of the present invention is to provide a chemically amplified resist having a high resolution and forming no T-shaped patterns.